What is the cut-off level for severity of Red Blood Cell (RBC) count in urine?

Red Blood Cell Count in Urine: Cut-off Levels for Severity

Microhematuria is defined as greater than 3 red blood cells per high-power field (RBC/HPF) on microscopic evaluation of a single, properly collected urine specimen. 1

Definition and Diagnosis of Hematuria

• Microscopic hematuria should be defined as >3 RBC/HPF on microscopic evaluation of urinary sediment from a properly collected urine specimen 1
• Dipstick testing alone is insufficient for diagnosis and should be confirmed by microscopic evaluation of urinary sediment 1
• A positive urine dipstick test (trace blood or greater) should prompt formal microscopic evaluation of the urine 1
• Quantitative reporting of RBC/HPF is important to determine whether further evaluation is warranted 1

Risk Stratification Based on RBC Count

The American Urological Association (AUA) and Society of Urodynamics, Female Pelvic Medicine & Urogenital Reconstruction (SUFU) guidelines stratify risk based on RBC count:

Low/Negligible Risk (0%-0.4% risk of malignancy)

• 3-10 RBC/HPF 1
• Patients with this level who are younger (women <60 years, men <40 years) and have no other risk factors 1

Intermediate Risk (0.2%-3.1% risk of malignancy)

• 11-25 RBC/HPF 1
• Patients with this level who have moderate risk factors (women ≥60 years, men 40-59 years) 1

High Risk (1.3%-6.3% risk of malignancy)

• 25 RBC/HPF 1

• Patients with this level who have significant risk factors (men ≥60 years, smoking history >30 pack-years) 1

Clinical Significance and Evaluation

• The degree of hematuria correlates with the risk of underlying pathology, particularly malignancy 1
• Even low levels of hematuria (3-10 RBC/HPF) warrant evaluation in high-risk patients 1
• Patients with >3 RBC/HPF from two of three properly collected urine specimens should be considered to have microhematuria requiring appropriate evaluation 1
• The prevalence of asymptomatic microscopic hematuria varies from 0.19% to as high as 21% in population studies 1

Special Considerations

Age and Gender

• In patients <40 years old, the risk of malignancy is significantly lower 2
• Men ≥60 years have higher risk of malignancy with any degree of hematuria 1
• Women <60 years have very low risk of malignancy in the absence of other risk factors 1

Risk Factors

• Smoking history (especially >30 pack-years) significantly increases risk 1
• Occupational exposure to chemicals or dyes (benzenes or aromatic amines) 1
• History of gross hematuria 1
• History of urologic disorders 1

Pitfalls and Caveats

• The sensitivity of the high-power field method in detecting RBCs has limitations, with sensitivity of only 63% for detecting ≥2,000 RBCs/ml unspun urine 3
• There is wide variation in RBC counts/ml for each degree of microscopic hematuria as defined by the HPF method 3
• Patients on anticoagulants should be assessed in the same fashion as patients who are not anticoagulated, as they have similar malignancy risk 1
• Dipstick testing has limited specificity (65-99% for 2-5 RBC/HPF) and can be confounded by factors such as povidone iodine use, myoglobinuria, and dehydration 1

Evaluation Algorithm

1. Confirm hematuria with microscopic examination (>3 RBC/HPF)
2. Assess risk factors (age, gender, smoking history, occupational exposures)
3. Categorize as low/negligible, intermediate, or high risk based on RBC count and risk factors
4. For low-risk patients: Consider repeat urinalysis in 6 months or cystoscopy with urinary tract ultrasound 4
5. For intermediate-risk patients: Recommend cystoscopy and urinary tract ultrasound 4
6. For high-risk patients: Recommend cystoscopy and axial upper urinary tract imaging 4

Remember that the cut-off of >3 RBC/HPF is the established threshold for defining microhematuria, but the clinical significance and evaluation pathway depend on the degree of hematuria (3-10,11-25, or >25 RBC/HPF) combined with patient risk factors.